Aquarius is a highly mobile miniqueen with coverage very similar to berserker with added bonuses of being able to freeze a target and also freeze its adjacent enemies. Edit
It can be used as a shorter rook or as a kind of short ranged comet. Its passive, which allows it to push and freeze all adjacent enemies away after self destructing, can be surprising and effective. Aquarius++ gets rid of an important weakness, namely its diagonal blindspot. It's a very usable and decent piece. But at +++ Aquarius reaches its full potential. It gains range diagonally and orthogonally, making it extremely powerful.
At base its limited range is a weakness, so it isn't terribly useful. At the + tier its increased range helps it to be a better piece, as does the increased freeze range. However, it may be slightly overpriced. While with the increased price it may not be worth self destructing, it can still be used to freeze other powerful units such as queen or King.